Step 1

Place onions, celery and carrot in a gallon-size sealable plastic bag and place in the freezer. Add vegetable and herb trimmings until the bag is filled.

Step 2

Place the vegetable-herb mixture in a large pot. Add water (add more, if needed to cover vegetables), peppercorns and bay leaves. Bring to boil; reduce heat to a gentle simmer. Simmer, partially covered, without stirring, until the vegetables are very soft and the liquid is golden brown, about 2 hours.

Step 3

Line a strainer with cheesecloth and place it over a large bowl. Carefully pour the liquid through the strainer to collect the solids and any grit at the bottom of the pan. Press the vegetables into the strainer to extract any liquid. Let cool, then refrigerate or freeze for future use.